The U.S. populace has been way to the left of the leadership for as long as I can remember, and with a pivot on culture-war issues the GOP could outflank today's Democratic party on populist/labor issues.
I don't think they're going to, but they could.
Either way, both parties have to take a big leap to the left, and I don't see the Democrats doing it yet.
If I recall correctly, soon after taking office, California's A.G. Jerry Brown was tasked with defending California's state DOMA law.
He did so, but he took a rather unusual legal tack, saying that marriage is not a fundamental right in California.
The strange thing is that the California Supreme Court had stated (in Perez v. Sharp, the ruling invalidating California's anti-miscegenation law, before Loving v. Virginia deemed those laws unconstitutional nationwide) and had affirmed and reaffirmed that marriage is a fundamental right in California.
The California Supreme Court was not swayed by the A.G.'s unusual argument, and declared the state's DOMA unconstitutional in "In Re: Marriage Cases" last year. (And we all know what happened after that.)
Dare we hope that Obama's DOJ is coming up with bizarre and legally unsound arguments for DOMA, or at least bizarre and uncomfortable ways of phrasing arguments, to "heighten the contradictions" and make it easy to overturn?